1. Field of the Invention
The present invention relates to a method and apparatus for reducing blind spots in obstacle detection when a vehicle is moving in reverse by making use of a channel switching means and appropriate control of signal transmission time.
2. Description of Related Arts
A conventional rear transducer is activated when the vehicle moves in reverse to search for any obstacles and informs the driver how close the vehicle is to the obstacle by an electronic detection process. The warning system is implemented by setting up multiple predetermined threshold values that will be compared with the distance measured from the transducer to an obstacle. The transducer then sounds an alarm at different frequencies to inform drivers of the actual distance from an obstacle. When the vehicle is very close to the obstacle or in imminent danger of collision with the obstacle, the transducer uses a short and rapid beeping sound to warn drivers.
With reference to FIG. 4, the transducer generally installed on the rear end of a vehicle emits ultrasonic signals radiating outward in a fan pattern. The ranges for ideal detection are divided into multiple zones, where the closest distance (a1) from either Transducer A or Transducer B to an obstacle falls in the first zone, and the next closest (a2) and third to closest distances (a3) fall in a second zone and third zone respectively, and the longest distance (a4) falls in a fourth zone.
Ultrasonic signals emitted from the transducers do not travel in straight lines but in waves, and the signals fan out from the transmission source. When an obstacle is detected in the overlapping region (b1) or in the outer corner of the fan-out range (b2), the transducer will probably mistakenly sense that the obstacle is in the second zone (a2) from the vehicle. Thus incorrect information will be provided to the driver with regard to the actual location of the obstacle. When an obstacle is located between two transducers and inside the overlapping beams of a region (b1), in other words not detected by either transducer, the obstacle is in a “blind spot” and will be completely undetected by the transducers.
Serious problems in obstacle detection have arisen when a vehicle is moving in reverse, especially when an obstacle is located in the first zone (a1). Any error in or failure of the transducer detection could lead to serious personal injuries or property damage. To avoid such mishaps, blind spots (b1, b2, and b3) must be reduced to an insignificant proportion in the whole detection range. With reference to FIG. 5, modifying the detection pattern of a transducer from a fan shape to a somewhat oval shape will reduce the proportion of blind spots in the detection range considerably. Therefore, the chance of erroneous and missed detection can be cut down.
With reference to FIG. 6, the detection pattern of a vehicle transducer is fan shaped. Transducer A sends out ultrasonic signals and receives the same echoed signals back from an obstacle. Then, Transducer B sends out ultrasonic signals and also receives the same echoed signals back. The transducer control circuit receives the echoed signals and records the time from the transmission of the signals to the reception of signals echoed back from an obstacle. The elapsed time is then used to calculate the closest distance between an obstacle and the vehicle. Transducer B follows the same process to emit signals and receive signals returned from an obstacle. The transmission durations for signals to travel from the transducers to an obstacle and return to the transducers are respectively recorded for calculation of the closest distance between the transducers and the obstacle. For reference, the transmission speed of ultrasonic waves through the air is 340 m/s. When the transducer overlap region (b1) is being scanned, Transducer A emits ultrasonic signals and later receives the same signals reflected from an obstacle, and then Transducer B emits signals and receives the echoed signals. The duration for signal transmission for both transducers are recorded for calculation of the closest distance from any transducer to an obstacle. Since a rear transducer cannot cover region b3, the area in region b3 must be reduced if the transducer is to maintain high accuracy in obstacle detection.